Bone screw and bone screw with holding element

ABSTRACT

A bone screw is provided, with a thread section ( 2 ) of tubular construction having a tip ( 3 ) at its first end and a second end opposite the latter. The tubular thread section ( 2 ) comprises a bone thread ( 22 ) on its outer wall, and the wall of the thread section ( 2 ) comprises a plurality of recesses ( 21 ). The bone screw further includes a holding element ( 4, 6 ) with a first section ( 41, 61 ) for connection to the thread section ( 2 ) and with a rod-like second section ( 43, 63 ) which in the inserted state of the holding element ( 4, 6 ) protrudes beyond the second end of the thread section ( 2 ). A stop is provided for limiting the distance of insertion of the holding element ( 4, 6 ) in the thread section ( 2 ). The holding element ( 4, 6 ) comprises an element ( 44, 64 ) at its free end for engagement with a screw-in tool.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of Application No. 10/680,706 filedOct. 6, 2003 now U.S. Pat. No. 7,736,381, which claims priority to andthe benefit of German Patent Application No. 102 46 386.7 filed on Oct.4, 2002, the disclosures of which are fully incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a bone screw, in particular to a bonescrew with a thread section having a periphery with an open net-like ormesh-like structure.

BACKGROUND OF THE INVENTION

A bone screw having a tubular wall with a plurality of recesses isdescribed in DE 100 55 891 A1. It includes a thread section, a tip atone end and a head for engagement with a screwdriver at the other end.The thread section of the tubular wall also comprises the plurality ofrecesses.

This bone screw can be used e.g. in the treatment of osteoporoticfractures. On account of the open mesh (or net-like) design of thescrew, fusion with surrounding bone material can take place.

A problem can be encountered when the position of the fracture in thebone, which e.g. in the hipbone is far away from the surface from whichthe screw is screwed in. In such situation, for reliable fixation,precise positioning of the bone screw is required and, sometimes, amechanical connection to external and/or internal bracing implants alsomay be required.

A bone screw system including a cannulated bone screw and an adapterdesigned to be releasably coupled to the screw is known from U.S. Pat.No. 6,048,343. The bone screw has a head with a diameter which is largerthan the diameter of the shaft of the screw. The largest diameter of theadapter is also greater than the diameter of the shaft of the bonescrew. Thus the bone screw cannot be placed at a fracture which is at alocation far away from the surface of the bone. DE 199 49 285 A1discloses a similar bone screw system including a bone screw and anadapter.

SUMMARY OF THE INVENTION

The present invention provides a bone screw with a thread section havinga periphery with an open mesh (or net-like) structure and a bonefixation device with improved properties. Preferred bone screws of thepresent invention can be positioned precisely and, optionally, also canbe connected to external and/or internal bracing implants.

In accord with one embodiment of the present invention, a bone screwcomprises a thread section of tubular construction having a tip at itsfirst end, a second end opposite the latter, and a holding element witha first section for connection to the second end of the thread sectionand a rod-like second section which, in the inserted state of theholding element, protrudes beyond the second end of the thread section.The tubular thread section comprises a bone thread on its outer wall andthe outer wall of the thread section comprises a plurality of recessesproviding an open mesh structure. Preferably, a stop is provided forlimiting the distance of insertion of the holding element into thethread section.

In another embodiment of the invention, the bone screw comprises athread section of tubular construction having a tip at its first end anda second end opposite the latter and, adjoining the second end of thethread section, a section free of bone thread and integral with thethread section. At the end of the adjoining section free of bone threadopposite the tip, preferably, a means for engagement with a screw-intool and/or a means for attaching a fixation element is provided. Thetubular thread section comprises a bone thread on its outer wall and thewall of the thread section comprises a plurality of recesses providingan open mesh structure.

In a preferred embodiment, the fixation element comprises a fixationplate with a hole or recess through which the free end of the rod-likeholding element can be passed, and the attaching means comprises a nutfor screwing onto the holding element from its free end for fixing theplate.

The invention also provides a bone fixation device comprising at leastone bone screw as described herein and a marrow nail for fixing a bone,the marrow nail having a borehole through which the free end of therod-like holding element can be passed.

Certain preferred embodiments of the bone screws of the presentinvention comprise one or more of the following (wherein references tothe drawings are provided as merely exemplary): the thread section 2 oftubular construction comprises an internal thread section 24 at itssecond end and the first section 41, 61 of the holding element 4, 6comprises an external thread for screwing into the internal threadsection 24; the connection between the holding element 4, 6 and thethread section 2 is made in the form of an interference fit; the holdingelement 4, 6 comprises an element 44, 64 at its free end for engagementwith a screw-in tool; the stop is provided in the form of a shoulder 42,62 between the first section 41, 61 and the second section 43, 63 of theholding element; the stop is provided in the tubular thread section 2 ofthe bone screw 1; the rod-like section 43, 63 of the holding element 4,6 comprises an external thread for screwing on a nut 83 from the freeend of the holding element 4, 6; the thread section 2 of tubularconstruction comprises an internal thread section 23 at its first end;the thread section 2 of tubular construction comprises an internalthread section 23 that extends over the whole length of the threadsection 2 of the tubular construction and the tip 3, 5, 7 at the firstend of the thread section 2 can be screwed into this internal threadsection 23; the internal thread section 23, 24 is designed andstructured as a metric or inch thread; the tip 7 is designed andstructured as a self-tapping tip; the tip 5 is cannulated (i.e.,comprises a cannula); the holding element 6 is cannulated; and/or thelength of the section 13 free of bone thread is the same as or greaterthan that of the thread section 12.

The invention further provides a holding element 4, 6 for attaching to abone screw, wherein the bone screw comprises a tip at its first end and,at the second end opposite the latter, a section for connection to theholding element. The holding element comprises a first section 41, 61for connection to the bone screw, a rod-like second section 43, 63 and,preferentially, a stop for limiting the distance of insertion of theholding element 4, 6 into the bone screw. Thus, when the holding elementis inserted into the bone screw, the rod-like second section 43, 63 ofthe holding element 4, 6 in the inserted state protrudes beyond thesecond end of the bone screw.

Preferably, the holding element comprises an external thread forscrewing into an internal thread section of the bone screw or theconnection between the holding element and the bone screw is made in theform of an interference fit.

The bone screw according to preferred embodiments of the invention hasan advantage that it can be immersed to the required location in thebone. Thus, it can fulfil its function as a tension element, without apart protruding from the bone (for example, see FIG. 3 b).

The invention also provides a method for repairing a bone having afracture. The method comprises providing a bone screw as describedherein, fully introducing the bone screw into the bone and positioningthe bone screw at the place of fracture, and attaching the holdingelement to a bone fixation device. Preferably, the bone fixation devicecomprises a plate or a marrow nail. In preferred embodiments, beforeattaching the bone fixation device, the method also includes removingthe holding element from the bone screw, applying a filler material intothe interior of the thread section of the bone screw and reconnectingthe holding element to the thread section.

Bone cement or reagents can be placed precisely by means of the bonescrew.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention are shown by thedescription of embodiments with the aid of the attached drawingswherein:

FIG. 1 illustrates an exploded view with several embodiments of amodular structure of a bone screw according to the present invention;

FIG. 2 illustrates a bone screw, as shown in FIG. 1, in the assembledstate;

FIG. 3 a to FIG. 3 c illustrate a sequence of steps for attaching anouter plate to a bone;

FIG. 4 illustrates a view of a combination of the bone screw with amarrow nail;

FIG. 5 illustrates a bone screw according to another embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

A bone screw according to a preferred embodiment of the presentinvention now will be described with reference to FIGS. 1 and 2. Part ofthe bone screw is shown in section in FIG. 2 to improve the clarity.

The modular bone screw shown in FIGS. 1 and 2 includes a thread section2, a tip 3 and a holding element 4. The thread section 2 is of tubularconstruction and contains in its wall a plurality of recesses 21 whichare diamond-shaped in the embodiment as shown and provide an open meshstructure. The diamond-shaped recesses are oriented in such a way thatan axis of symmetry extends parallel to the axis of symmetry orlongitudinal axis of the tube respectively. The diamonds also arestaggered from each other.

On the outer surface of the wall there is provided a so-called bonethread 22 which corresponds in shape to that of the usual bone screwsthat are well known to those skilled in the art. On the inner surface ofthe wall, the tubular thread section 2 comprises at each of its two endsan internal thread 23, 24, e.g., a metric thread.

The tip 3 includes a shank portion 32 and the actual tip portion 31having tapered sides. In the embodiment shown, the shank 32 comprises anexternal thread which corresponds to the internal thread 23 of thetubular thread section 2 for connection of the tip 3 to the threadsection 2, as shown in FIG. 2.

The holding element 4 comprises at a first end a first section 41 withan external thread which corresponds to the internal thread 23 of thetubular thread section 2 for connection of the holding element 4 to thethread section 2, as shown in FIG. 2. At the end of the thread section41, a stop 42 is provided in the form of a shoulder or annularprojection from the outer surface. The stop limits the screw-in distancewhen assembling the holding element 4 with the thread section 2. As canbe seen in particular from FIG. 2, the outer diameter of the annularprojection of stop 42 preferably corresponds to the outer diameter ofthe tubular thread section 2, so that it does not form an obstacle inthe bone opening when the bone screw is screwed into the bone.

The holding element further comprises a rod-like section 43 which, asshown in FIG. 2, protrudes beyond the second end of the thread section 2of the assembly. The rod-like section 43 preferably is providedcontinuously with a metric external thread. The axial length of therod-like second section 43 preferably is longer than that of the firstsection 41, which is to be screwed into the thread section 2. Due to themodular construction of the bone fixation device, the length of theholding element can be selected by the surgeon at the place of use ofthe bone screw in such a way that the tubular thread section 2 can beimmersed to the required location in the bone.

At its free end opposite the section 41, the holding element comprisesan engagement element for a screw-in tool in the form of a hexagonshaped outer surface 44. However, the engagement element can be astructure that corresponds to any standard or non-standard driving toolfor turning the bone fixation assembly.

The thread section 2, the tip 3 and the holding element 4 are formedpreferably from titanium. However, any other biocompatible material canbe used providing it has sufficient strength properties for use in abone fixation application.

Use of the bone screw now is described with reference to FIGS. 2 and 3.The bone screw 1, e.g., is inserted into the end of a long bone which isweakened from the inside by osteoporosis, e.g., in the neck of a femur.

The fixation device is assembled, first, by screwing the tip 3 into thetubular thread section 2. Next, the holding element 4 is screwed intothe thread section 2. As a result the structure shown in FIG. 2 isobtained.

Next, as shown in FIG. 3 a, the bone screw 1 composed of thread section2, tip 3 and holding element 4 is screwed into the bone. In the process,the thread section 2 can be immersed deep in the bone and at the sametime positioned precisely at the place of fracture. Then, the holdingelement 4 is unscrewed and removed from the thread section 2.

In a further step, such as depicted in FIG. 3 b, a filler material suchas bone cement or the like and/or a medicinal or growth-promotingreagent, if desired, can be injected into the interior of the threadsection 2. By contrast with direct injection, the thread section 2ensures more accurate positioning of the injection channel and more evendistribution of the injected material which can exit through therecesses 21 into the adjacent sections of the bone. As a result,fixation of the bone by the screw can be improved further.

The immersed bone screw serves as a reinforcement for the bonetrabeculae weakened e.g. by osteoporosis. Through the recesses 21, thebone can grow into the screw. Stabilization of the fracture point of theweakened bone, thus, takes place as a combination of tension relief andfusion.

FIG. 3 c illustrates the use of an outer fixation plate 81 as a fixationdevice 80 for fixation of the bone. Here, after injection of the fillermaterial, if desired, the holding element 4 is screwed back into thethread section 2. The plate 81 with a recess (or through-hole) 82 isapplied to the bone in such a way that the free end of the holdingelement 4 extends through the recess 82, and the plate 81 is rigidlyconnected to the bone screw 1 by screwing a nut 83 onto the externalthread of the rod-like section 43 of the holding element 4. Further,bone screws 84 can be added to serve for a stable fixation of the plate81 to the bone. The rod-like section 43 the holding element 4 preferablycan be shortened to a finished length such that it does not protrudesubstantially beyond the nut 83.

FIG. 4 shows a further example of application of the bone screwaccording to the first embodiment. With the fixation device 90, fixationof the bone takes place not by means of an outer fixation plate but,instead, by means of a marrow nail 91 introduced into the bone. Themarrow nail 91 comprises at least one recess (or bore hole) 92 throughwhich extends at least one holding element 4 of a bone screw 1. In theembodiment shown in FIG. 4, there are two bone screws 1 with differentdiameters. A closure screw 93 closes the marrow nail against theoutside, and a locking screw 94 prevents movement in the longitudinaldirection.

A second embodiment of the modular bone screw 1 shown in FIG. 1 differsfrom the first embodiment in that, instead of the tip 3, a cannulatedtip 5 is provided. Further, in this embodiment the holding element is acannulated holding element 6. The cannulated tip 5 differs from the tip3 in that, in addition, a coaxial bore 53 for passage of a reagent isprovided. The cannulated holding element 6 differs from the holdingelement 4 in that, in addition, a coaxial bore 65 is provided and inthat the rod-like section 63 is not provided with a metric thread overits whole length like the rod-like section 43 in the first embodiment,but only in a partial section 66.

All other characteristics of this second embodiment match the firstembodiment, and use of the device also takes place in the same way. Thisembodiment has the advantage that, even without unscrewing the holdingelement and even after installation is completed, a medicinal reagentcan be introduced precisely to the desired location, e.g., by means of asyringe.

A third embodiment of the modular bone screw 1 shown in FIG. 1 differsfrom the first and second embodiments in that, instead of the tip 3, aself-tapping tip 7 is provided. All of the other characteristicscorrespond to the first or second embodiment, and use of this embodimenttakes place in the same way, as well. Introduction of the bone screwinto the bone can be easier by the self-tapping tip.

A fourth embodiment shown in FIG. 5 differs from the first to thirdembodiments shown in FIGS. 1 and 2 in the structure of the screwsection. The bone screw 10, in accord with the fourth embodiment,includes a screw section 11 and a tip. The screw section 11 is oftubular construction and consists of a thread section 12 and an integralsection 13 free of bone thread. Any of the tips 3, 5 and 7 described inthe first to third embodiments can be used as the tip.

The thread section 12, like the thread section 2 described in the firstembodiment, comprises in its circumferential wall a plurality ofrecesses 21 and, on its outer surface of the wall, a bone thread 22. Thesection 13, on the other hand, is formed without bone thread. In thisembodiment as shown, no recesses are formed in the wall in the section13, which is free of bone thread. However, in certain preferredembodiments, recesses can be provided here, too, to provide further openmesh structure.

On the inner surface of the wall, the tubular screw section 11 comprisespreferably at each of its two ends a metric internal thread 14, 15. Theaxial length of the section 13 (free of bone thread) is selected as afunction of the place of use of the bone screw in such a way that thethread section 12 can be immersed to the required location in the bone.The axial length of the section 13 also can be longer than the axiallength of the thread section 12.

The tubular screw section 11 is preferably formed from titanium.However, as stated above, any other biocompatible material havingsuitable strength properties can be used as well.

Use of the embodiment shown in FIG. 5 also takes place in the same wayas in the first to third embodiments, as described above. To screw thebone screw 10 into the bone, a holding element 4, 6 can be screwed intothe internal thread 15. The holding element can be removed later or canremain as an extender. Alternatively, a head with an engagement elementcan be inserted using thread 15 for engaging and cooperating with ascrew-in tool. The free end of the section 13 without bone thread canalso itself comprise an engagement element for a screw-in tool, e.g., across recess.

The embodiments described are only examples. Thread section, tip andholding element can be combined with each other not only as described inthe embodiments, but in many ways by those skilled in the art afterconsidering this disclosure. This modular structure allows adaptation tothe most varied demands.

The stop for limiting the distance of screwing the holding element 4, 6into the thread section 2 can be provided in the tubular thread section2 instead of on the holding element 4, 6, e.g. at the end of theinternal thread 24.

The holding element 4, 6 can be formed such that the rod-like section43, 63 comprises an external thread over its whole length as in thefirst embodiment, or only in a partial section as in the secondembodiment. Alternatively, the rod-like section 43, 63 can also beformed completely without an external thread. Further, the diameter ofthe rod-like section 43, 63 can, as shown in FIGS. 1 and 2, be the sameas that of the first section 41, 61 of the holding element 4, 6, but itcan also have a different, preferably smaller diameter. In addition, therod-like section can be made of a tubular construction, similar to thethread section.

The holding section 14 according to the fourth embodiment too can havean external thread over its whole length or only in a partial section asin the second embodiment.

Instead of the outer hexagon section 44, 64, any other shape or type ofengagement element for cooperating with a screw-in tool can be provided.Thus, the free end of the holding element 4, 6 alternatively can have,e.g., a recess for an Allen type wrench, too. The holding element 4, 6also can be designed without an engagement element 44, 64 for a screw-intool. The bone screw is then screwed in with a suitable tool whichengages with the rod-like section 43.

The thread sections 23, 24, 41, 43, 61, 66, 14 and 15 have beendescribed sometimes herein as metric in the embodiments. Alternatively,the threads can be inch threads or in some other suitable form.

Instead of the internal threads 23 and 24 or 14 and 15, a singleinternal thread which extends over the whole length of the threadsection 2 or screw section 11 can be formed (this also can be appliedfor holding element sections that are a tubular structure). This has theadvantage that the tubular material can be manufactured in long piecesand cut to any length, so that bone screws of the desired length can bemade at the site of use, and so stockkeeping of various lengths ofcomponents can be substantially reduced.

As an alternative to the diamond-shaped recesses 21, other shapes ofopening can be provided, in particular, round openings.

The tip 3, 5, 7 can be connected to the thread section 2 or 12 not onlyby screwing in. Alternatively, the first end of the thread section 2 or12 and the shank 32, 52, 72 of the tip 3, 5, 7 can be formed without therespective threads and defined in their dimensions such that the tip 3,5, 7 is rigidly connected to the thread section 2 or 12 in a snug fit orinterference fit. Further, alternatively, the tip 3, 5, 7 can beconnected rigidly to the thread section 2 or 12 in any other way. Thetip and thread section also can be formed integrally in one piece.

The holding element 4, 6, too, can be connected rigidly to the threadsection 2 or 12 in a snug (or interference) fit or in any other way.

As an alternative to the procedure shown in FIGS. 3 a) to c), thetubular thread section 2 can be filled, e.g., with bone material beforescrewing on the holding element. Then, the screw is immersed.

The screw can also remain in the immersed state without being connectedto a plate via a holding element.

The combination of tension relief and fusion described above withreference to FIGS. 3 a)-3 c) can of course be carried out not only inthe femur, as mentioned as an example, but also in any other bones,e.g., the tibia, etc.

The bone screw 1, 10 is not suitable only, as shown in the practicalexamples, for introduction into long bones. It can be used e.g. invertebrae or other bones as well.

The holding element 4, 6 can be used not only in combination with thetubular thread section 2, but also with any other form of bone screwswhich can be, e.g., solid or cannulated. The connection to other formsof bone screws is made in the same or a similar way as the connection tothe thread section 2 described above.

This invention has been described in detail including the preferredembodiments thereof. However, it will be appreciated that those skilledin the art, upon consideration of this disclosure, may makemodifications and improvements within the spirit and scope of thisinvention.

1. A method for repairing a bone having a fracture with a bone screwcomprising an elongated tube having a first end, a second end and atubular wall defining an interior opening extending from the first endto the second end, and a separate non-resorbable elongated holdingelement connected to the elongated tube at the second end, the elongatedtube further comprises a bone thread on an outside surface of thetubular wall and the tubular wall comprising a plurality of recessesthrough the tubular wall to the interior opening forming a mesh-likeopen network, the method comprising: immersing the entire elongated tubeinto the bone; positioning the elongated tube across t he fracture; andattaching a fixation device to the holding element.
 2. A methodaccording to claim 1, wherein the fixation device comprises a plate or amarrow nail.
 3. A method according to claim 1, further comprising:screwing a tip to the first end of the elongated tube; screwing theholding element to the second end of the elongated tube; and introducingthe holding element into the bone when the elongated tube is fullyintroduced into the bone.
 4. A method according to claim 3 furthercomprising applying a filler material into the interior opening of theelongated tube at a location adjacent the plurality of recesses.
 5. Amethod according to claim 4, wherein the filler material is applieduntil it contacts the bone through the plurality of recesses.
 6. Amethod according to claim 1, further comprising a tip connected to thefirst end of the elongated tube and wherein immersing the entireelongated tube into the bone includes immersing the entire tip into thebone.
 7. The method according to claim 1, further comprising using theholding element as a driving tool to move a tip of the elongated tubeacross the fracture.
 8. The method according to claim 1, furthercomprising: applying a filler material into the interior opening of theelongated tube of the bone screw; and then connecting the holdingelement to the elongated tube.
 9. A method for repairing a bone having afracture with a bone screw comprising an elongated tube having a firstend, a second end and a tubular wall defining an interior openingextending from the first end to the second end, and an elongated holdingelement connected to the elongated tube at the second end, the elongatedtube further comprises a bone thread on an outside surface of thetubular wall and the tubular wall comprising a plurality of recessesthrough the tubular wall to the interior opening forming a mesh-likeopen network, the method comprising: immersing the entire elongated tubeinto the bone; positioning the elongated tube across the fracture;attaching a fixation device to the holding element; and shortening theholding element.
 10. A method for repairing a bone having a fracturewith a bone screw comprising an elongated tube having a first end, asecond end and a tubular wall defining an interior opening extendingfrom the first end to the second end, and an elongated holding elementconnected to the elongated tube at the second end, the elongated tubefurther comprises a bone thread on an outside surface of the tubularwall and the tubular wall comprising a plurality of recesses through thetubular wall to the interior opening forming a mesh-like open network,the method comprising: immersing the entire elongated tube into thebone; positioning the elongated tube across the fracture; attaching afixation device to the holding element removing the holding element fromthe elongated tube after the immersing step; applying a filler materialinto the interior opening of the elongated tube of the bone screw; andreconnecting the holding element to the elongated tube.
 11. A method forrepairing a bone having a fracture with a bone screw comprising anelongated tube having a first end, a second end and a tubular walldefining an interior opening extending from the first end to the secondend, and an elongated holding element connected to the elongated tube atthe second end, the elongated tube further comprises a bone thread on anoutside surface of the tubular wall and the tubular wall comprising aplurality of recesses through the tubular wall to the interior openingforming a mesh-like open network, the method comprising: immersing theentire elongated tube into the bone; positioning the elongated tubeacross the fracture; and attaching a fixation device to the holdingelement by screwing a fastener to an end of the holding element tofasten the bone screw to the fixation device.
 12. A method for repairinga bone having a fracture with a bone screw comprising an elongated tubehaving a first end, a second end and a tubular wall defining an interioropening extending from the first end to the second end, and an elongatedholding element connected to the elongated tube at the second end, theelongated tube further comprises a bone thread on an outside surface ofthe tubular wall and the tubular wall comprising a plurality of recessesthrough the tubular wall to the interior opening forming a mesh-likeopen network, the method comprising: immersing the entire elongated tubeinto the bone; positioning the elongated tube across the fracture;attaching a fixation device to the holding element; and using theholding element as a driving tool to move a tip of the elongated tubeacross the fracture.
 13. The method according to claim 12, furthercomprising: applying a filler material into the interior opening of theelongated tube of the bone screw; and then connecting the holdingelement to the elongated tube.